The present invention relates to devices which can move freely in one direction along a rope, but which grab securely when loaded in the opposite direction. The device of the invention is useful as a self-belaying device for climbers, and a safety device for industrial applications.
The sport of climbing or mountaineering typically requires a team of two people. To ensure the safety of the climber, the climber ties into a rope (i.e. the rope is tied to a harness worn by the climber), and is belayed by a partner. While the climber ascends, the belayer takes up or lets out the rope such that the rope is maintained taut between the climber and belayer, preventing a fall of any great distance by the climber. One type of belaying system, known as "top-roping", employs an anchor placed at the top of the cliff. Typically, the rope runs through this anchor pulley-fashion and the belayer stands at the foot of the cliff, although in some cases the belayer will belay from the top. In either case, the anchor is above the climber at all times, so that the climber will fall only a short distance if he "falls off" the climb.
This safety system, employed correctly, is generally very effective. However, because a partner is not always available, there has been a need for a device which would protect the safety of the climber in a similar manner without the need for a second person to belay (such a device will be referred to hereinafter as a "self-belay device").
An effective self-belay device would also be advantageous in safeguarding workers who are required to climb on the job, for example carpenters, roofers and the like.
An effective self-belay device would be one which would slide freely up a rope which is anchored at the top of a cliff or building, but lock securely in place when loaded downward, e.g., if the climber should fall.
One type of device which has been tried for use as a self-belay device is an "ascender". These devices are intended for use in climbing a fixed rope, in situations in which it is preferable to climb the rope rather than the rock or ice cliff. In order to climb a fixed rope, a pair of ascenders is attached to the rope, and the climber ascends by moving one ascender at a time up the rope, and stepping up into a stirrup attached to that ascender. In this use, the ascender is relatively safe, as it is easy for the climber to ascertain whether the ascender will properly grab the rope before the climber commits his weight to the device, and if the ascender does not grab, the clamping mechanism can then be hand assisted. Further, the use of two ascenders allows the load to be transferred from one to the other gently, and the direction of the load is continuously, rather than suddenly, downward. However, for a number of reasons, this device is highly unsafe when used as a self-belay device in a free-climbing situation, i.e. when the climber is climbing the rock itself. For example, the downward load when the climber falls is sudden and may be many times the climber's weight; the orientation of the climber is unpredictable; it is critical that the device immediately grab; and loops of slack rope may form if the rope does not feed properly through the device.
Further, ascenders typically require moving parts, which increases the possibility of mechanical failure and jamming of the device with, e.g., snow, dirt and corrosion. Also, these devices typically utilize camming devices to lock the device against the rope, the teeth of which may become worn due to friction from the rope in a self-belay situation, causing them to become polished and not grab the rope during a fall.
Two devices have been manufactured specifically for use as self-belay devices. One, sold by Petzl under the tradename "SHUNT", is used primarily as a back-up safety device for rappeling (descending an anchored rope). The other, sold by Rock Exotica, under the tradename "SOLOIST", is used as a self-belay device for free climbing. Both devices, however, suffer from many of the same disadvantages as ascenders, for example moving parts, camming parts which place a high localized stress on the rope during a fall, and sensitivity to rope diameter. Most importantly, the "Soloist" device may fail to hold a fall if the orientation of the climber with respect to the rope anchor is such that the rope does not properly torque the camming device, while the "Shunt" device may inadvertantly be pulled down the rope, instead of locking in place, if it is improperly loaded during a fall.
Additionally, all of the above-mentioned devices are sensitive to rope diameter, and can only be used safely with ropes of diameters of from 9 to 11 mm.
A further deficiency of the prior art devices is the difficulty of descending the rope after having fallen while climbing a building or cliff. It is necessary when using such devices to attach a separate rappel device in order to descend, which is generally awkward and difficult due to the load on the self-belay device.
Thus, it has been desired in the climbing field, to provide a self-belay device which would be safe in a variety of climbing situations, would be free from moving parts, could be used with any diameter rope and could easily be used to descend the rope.